Järnsjöns fiskevårdsområdesförening (FVOF) was formed in 1992 and consists of approximately 500 fishing rights owners distributed over 38 households. Järnsjön, Svensbysjön and Ösjön have previously been their own fisheries conservation associations. Järnsjöns FVOF has primarily worked with biotope conservation and the construction of ponds. The association has spent a lot of time constructing pool stairs at the dams, Nedre Tvängen and Södra Tvängstjärn. The largest lake in the area is Järnsjön with its 1980ha and a maximum depth of 64 meters.

The lake is known for its large trout.